1. Field of the Invention
The present invention concerns a method of manufacturing UV-radiation absorbing glass, which has only reduced absorption in the visible range, and to the glass made by this method as well as to its use.
2. Description of the Related Art
Glasses with strong UV-absorbing properties are already known. These glasses are used for making gas discharge tubes and especially fluorescence lights and for making liquid crystal displays (LCDs). Fluorescent lights are used as light sources, especially in back side illuminated displays (so-called back light displays). This type of fluorescent light has very small dimensions and the lamp glass accordingly has only an extremely small thickness. It has been shown that the absorption in the visible range under 1000 nm is considerable despite the reduced thickness. This is disadvantageous, especially in a high-grade display device, such as an electronic display unit, for example a computer screen for laptops, or also in mobile telephones.
Moreover the permeability and/or transmission of especially visible light up to wavelength ranges under 400 nm, especially under 380 nm, is kept comparatively constant in glasses for this sort of application and then drops steeply. Gas discharge lamps, especially fluorescent lamps, emit a large fraction of their radiation in the UV range, which has a damaging effect for surrounding components, such as polymers and other plastic materials. Thus they become brittle after a certain time, which can lead to them becoming unusable. The mercury emission line at 318 nm is especially damaging. It is thus a goal to prepare glass of this type, which completely absorbs this emission line.
Furthermore fluorescent lamp glasses are known from U.S. Pat. No. 5,747,399 A for the above-described applications, which absorb UV-radiation in the desired amounts. However it has been shown that this sort of glass exhibits a strong solarization and a strong discoloration in the visible range. Frequently a yellow-brown coloration arises when the raw material for these lamp glasses melts.
A zirconium-oxide-containing and lithium-oxide-containing borosilicate glass of high resistance is known from DE-A 198 42 942, which is especially suitable for use as sealing glass for sealing with Fe—Co—Ni alloys. This sort of glass can also contained colored ingredients, such as Fe2O3, Cr2O3, CoO and TiO2.
In U.S. Pat. No. 4,565,791 A glass is described for opthalmologic applications, which has a special index of refraction and Abbé number, and a suitable density for that application. This sort of glass has a UV absorption limit or edge between 310 nm and 335 nm and contains TiO2 as UV absorber. For manufacture of this glass this reference expressly teaches that refining with chlorine is required, since refining with As2O3 and with Sb2O3 is not sufficient. Finally the reference teaches that although these glasses are extremely thin, a combination of Fe2O3 and TiO2 leads to a discoloration of the glass so that quartz raw material should be used exclusively with an iron content of less than 100 ppm.